I'm coming from a background in C and C , where I grew pretty comfortable with pointers and references. Now I'm learning Data Structures and Algorithms in Java, and I saw a slide talking about nodes in Linked Lists being structured as so

class Node<E>{
    E element;
    Node<E> next;
    public Node(E o){
        element = o;
    }
}

Given my background, to me this looks like the next node is contained directly within this node, and there's nothing to clarify that it's a reference (pointer?) to a separate address in memory. I also know at this point that Java doesn't have pass-by-reference at all, which makes this even weirder (from my perspective). So I want to know, how do I tell the difference between variables that hold actual values or objects, and variables that hold references to other values/objects

CodePudding user response：

In Java, unlike C or C , all variables with types that are not primitives are references. In this case, next is a reference because Node is an object, not a primitive. element would also be a reference to another object, unless E is a primitive. Java's garbage collector handles all the memory management for these references, so you don't need to worry about allocation and freeing the memory for the underlying objects. For example:

Foo bar = new Foo();    // bar is an object of the class Foo
Foo foobar = bar;       // all objects are references, so bar and foobar are
                        // referencing the same underlying memory

int a = 1;              // a is an int
int b = a;              // the value of a is copied into b, because a is a 
                        // primitive

CodePudding user response：

In Java, variables fall into two categories.

• primitives (int, short, boolean, char, long, byte, double, float),
• references (everything else).

The type parameter E can't be a primitive type in this context, so in your code, element and next both store references to something. That's why your class succeeds in implementing a linked list.

As for the question of how this works with "pass by value" - argument values passed to a method are either primitives or references, just like the values of any other Java variable. So if your parameter is a reference type, not a primitive; then although you're doing "pass by value", it behaves a little like "pass by reference", insofar as the method being called now has access to the original object, not a copy. Of course, it's not really "pass by reference" because the method that was called can't change what the original variable refers to.

CodePudding user response：

Variables in Java are classified into primitive and reference variables. From the programmer's perspective, a primitive variable's information is stored as the value of that variable, whereas a reference variable holds a reference to information related to that variable. reference variables are practically always objects in Java. Let's take a look at both of these types with the help of two examples.